Effects of ultra-low volume applications of malathion in Hale County, Texas. II. Mosquito populations in treated and untreated areas.

Abstract

The effects of ultra-low volume (ULV) aerial applications of technical malathion at the rate of 214 g/ha (3 oz. per acre) on mosquito populations was evaluated in 3 Hale County, Texas towns during June through August, 1967. Light trap and sentinel shed trap indices were used to follow trends in adult mosquito population fluctuations in the treated towns and in I untreated town and selected rural sites. Four species, Aedes nigromaculis (Ludl.), Aedes vexans (Meig.), Gulex tarsalis Coq., and Psorophora signipennis (Theob.), made up 99% of the mosquitoes collected in light traps. Only 3 species, A. vexans, C. tarsalis , and Gulex pipiens quinquefasciatus Say, were commonly collected in chicken-baited sentinel shed traps. An evaluation of the effects of ULV aerial treatments with malathion on mosquito populations was made by comparing pre- and post-treatment population indices. These comparisons indicated that lasting mosquito control was not achieved. Although Substantial reductions were some times obtained by treating, there was evidence that G. tarsalis populations in Plainview returned to their pre-treatment levels by the third day following treatment, and that Psorophora and Aedes spp. did so by the fourth and fifth days, respectively. It was apparent also that mosquito populations built up and declined on a seasonal basis independently of the treatments. Infiltration of adult mosquitoes from outside the treated areas was postulated to account for the rapid post-treatment population build-ups.